Add messageReference

Author: tdroza-nhs

src/cloudevents/domains/digital-letters/2025-10-draft/data/digital-letters-print-letter-transitioned-data.schema.yaml

@@ -6,6 +6,8 @@ additionalProperties: false
 properties:
   subject:
     $ref: ../defs/print.schema.yaml#/properties/subject
+  messageReference:
+    $ref: ../defs/requests.schema.yaml#/properties/messageReference
   status:
     $ref: ../defs/print.schema.yaml#/properties/status
   supplierId:
@@ -14,6 +16,7 @@ properties:
     $ref: ../defs/print.schema.yaml#/properties/time
 required:
   - subject
+  - messageReference
   - status
   - supplierId
   - time